Tropical Race Research Articles

Suppression of Banana Fusarium Wilt Disease with Soil Microbial Mechanisms via Pineapple Rotation and Residue Amendment

The large outbreak of banana Fusarium wilt has become a bottleneck limiting the industry’s development, and crop rotation is a cost-effective and essential measure to overcome the obstacles of banana crop monoculture. The present work was carried out to explore the mechanisms of how changes in soil chemical properties and the reestablishment of soil microorganisms in high-incidence soils are affected by crop rotation and plant residue. In this study, pineapple–banana crop rotation and pineapple residue amendment were carried out to alleviate banana Fusarium wilt, and their effects on bacterial and fungal communities were analyzed using the MiSeq Illumina sequencing platform. Both pineapple–banana rotation and residue addition significantly reduced disease incidence. Moreover, pineapple rotation and residue amendment altered the bacterial and fungal community composition. The taxonomic and phylogenetic alpha diversity of bacteria and fungi significantly increased against disease suppression and nutrition competition. The relative abundances of the Burkholderia, Pseudomonas, Elaphocordyceps, Penicillium, and Talaromyces genera were higher, and the number of Fusarium was significantly lower in rotational soil than in banana monoculture soil. Finally, linear models (LM) showed that the Burkholderia and Talaromyces in crop rotation, and Aspergillus in residue amendment had a significantly negative relationship to disease incidence, which plays a key role in Fusarium reduction. To consider the economic benefits and protect the vitality of the soil, this study suggested that pineapple–banana rotation and pineapple residue amendment both could be considered for the sustainable management of banana wilt.

Estimating worldwide benefits from improved bananas resistant to Fusarium Wilt Tropical race 4

AbstractWe assess the economic welfare implications of developing and introducing a gene‐edited banana with resistance against an emerging plant disease, Fusarium oxysporum f.sp. cubense Tropical race 4, on global banana production. Using a model incorporating disease dynamics and diffusion of a technological solution, we find that a 5‐year delay in adoption results in discounted losses of $94 billion. Consumers always lose from delay, while the impact on producers depends on timing and severity of the disease. The results suggest that regulatory delay significantly decreases return on investment from research, and acceptance of a technological solution may depend on the distribution of benefits and costs across stakeholders.

Spatiotemporal biocontrol and rhizosphere microbiome analysis of Fusarium wilt of banana

The soil-borne fungus Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes Fusarium wilt of banana (FWB), which devastates banana production worldwide. Biocontrol is considered to be the most efficient approach to reducing FWB. Here we introduce an approach that spatiotemporally applies Piriformospore indica and Streptomyces morookaensis strains according to their respective strength to increase biocontrol efficacy of FWB. P. indica successfully colonizes banana roots, promotes lateral root formation, inhibits Foc TR4 growth inside the banana plants and reduces FWB. S. morookaensis strain Sm4-1986 secretes different secondary compounds, of which xerucitrinin A (XcA) and 6-pentyl-α-pyrone (6-PP) show the strongest anti-Foc TR4 activity. XcA chelates iron, an essential nutrient in pathogen-plant interaction that determines the output of FWB. 6-PP, a volatile organic compound, inhibits Foc TR4 germination and promotes banana growth. Biocontrol trials in the field demonstrated that application of S. morookaensis lead to improvement of soil properties and increase of rhizosphere-associated microbes that are beneficial to banana growth, which significantly reduces disease incidence of FWB. Our study suggests that optimal utilization of the two biocontrol strains increases efficacy of biocontrol and that regulating iron accessibility in the rhizosphere is a promising strategy to control FWB.

Transcriptome and metabolome profiling provide insights into hormone-mediated enhanced growth in autotetraploid seedlings of banana (Musa spp.)

IntroductionReconstructive breeding based on autotetraploids to generate triploid varieties is a promising breeding strategy in banana (Musa spp.). Therefore understanding the molecular mechanisms underlying the phenotypic differences between the original diploid and its autopolyploid derivatives is of significant importance in such breeding programs of banana.MethodsIn this study, a number of non-chimeric autotetraploid plants, confirmed by flow cytometry and chromosome counting were obtained using colchicine treatment of ‘Pisang Berlin' (AA Group), a diploid banana cultivar highly resistant to Fusarium wilt Tropical Race 4 (Foc TR4) and widely cultivated in Asia.Results and discussionThe autotetraploids showed significant increase in plant height, pseudostem diameter, root length, leaf thickness, leaf area, and leaf chlorophyll content. Transcriptomic analysis indicated that differentially expressed genes were mainly enriched in plant hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling pathway, and carbon fixation in photosynthetic organelles. The genes related to the metabolism, transport or signaling of auxin, abscisic acid (ABA), cytokinin (CTK) and gibberellin (GA), as well as the genes encoding essential enzymes in photosynthetic CO2 fixation were differentially expressed in leaves of autotetraploids and most of them were up-regulated. Metabolomic analysis revealed that the differentially accumulated metabolites were mainly involved in plant hormone signal transduction, porphyrin and chlorophyll metabolism, indole alkaloid biosynthesis, and carbon fixation in photosynthetic organelles. The results therefore, demonstrate that the hormones IAA, ABA, and photosynthetic regulation may play a vital role in the observed enhancement in the autotetraploids. These could be used as molecular and biochemical markers to facilitate the generation of triploid progenies as suitable new varieties for cultivation.

In-vitro screening of antagonistic potential of native endophyte strains of banana (Musa spp.) against Fusarium oxysporum f. sp. cubense TR4 causing Fusarium wilt of banana

The experiment was done in the Department of Plant Pathology, RPCAU, Pusa, Bihar during 2021-22 to identify the antagonistic potential of native endophytes of bananas against FocTR4. An in-vitro investigation revealed that only four bacterial endophytes, GNBE4, GNBE9, GNBE12, and GNBE14, showed significant antagonistic effects against FocTR4out of 18 screened endophytes (13 bacterial and 5 fungal) of banana. The GNBE4 (Alcaligens sp.) showed maximum mycelial inhibition (75.18%), followed by GNBE9 (Stenotrophomonas maltophilia) (71.90%) and GNBE12 (Staphylococcus warneri) (70.69%), while lowest in GNBE14 (Bacillus subtilis) (61.07%). Among the fungal endophytes, the maximum mycelial growth inhibition was shown in RzFE and LfFE (42.78%) followed by PsdFE (36.11%), while lowest in PtFE1 (26.67%). Apart from that already identified antagonistic PGPR like Pseudomonas fluorescens was obtained from the Department of Microbiology were tested which significantly suppressed the mycelial growth of fungus having a mycelial inhibition of 70.01 %.

An Interactive, Online Web Map Resource of Global Fusarium oxysporum ff. spp. Diversity and Distribution.

An Interactive, Online Web Map Resource of Global Fusarium oxysporum ff. spp. Diversity and Distribution.

In vitro inhibition of bacteria against Fusarium oxysporum f. sp. cubense race 2

There are three races of Fusarium oxysporum f. sp. cubense (Foc) that affect bananas and plantains, though the Cavendish group banana cultivars are resistant to Foc race 1 (FocR1) and Foc race 2 (FocR2). However, there are no effective control methods for the Tropical Race 4 (R4T). The foregoing makes it necessary to generate biological control strategies for FocR2 fungal model that is present in Mexico, forecasting the potential introduction of FocR4T into our country. In vitro inhibition was evaluated of bacterial strains Bacillus subtilis (BASU), B. velezensis (BAVE), and B. sonorensis (BASO) against three isolates of FocR2 (MIC17188, MIC17191 and MIC17192), obtained from plant samples collected in three banana production sites in the states of Puebla, Michoacán and Oaxaca. At 14 days, the strain BASU had in average high inhibition (55.1%) in comparison to BAVE and BASO strains (45.8 and 21.7%, respectively) against the three fungal strains mentioned before. In addition, the in vitro inhibition of Paenibacillus sp. (BSP 1.1) and Serratia sp. (AC35) was also evaluated by considering three pre-inoculation timings; the strain BSP1.1 showed high inhibition (80.1%) when pre-inoculated individually seven days before the fungus and at seven days of confrontation.

Synthesis and anti-bacterial/fungal activities of amphiphilic polysiloxanes primary ammonium salts

Amphiphilic cationic polymers are currently used as antimicrobial agents to disrupt microbial membranes with long-termed stability and low bio-toxicity. However, there are few studies on the relationship between molecular structure and antimicrobial properties of amphiphilic polymers containing primary amine salts against fungi. In this work, a series of polysiloxanes graft primary ammonium salts (PDMS-g-AH) with tunable molecular weights (3 kDa, 5 kDa, 8 kDa, and 10 kDa) and grafting ratios (50% and 75%) were synthesized via thiol-ene “click reaction”, and the effect of their structural parameters on the broad-spectrum inhibition of bacteria (Escherichia coli and Staphylococcus albus) and pathogenic fungi (Candida albicans), especially on two phytopathogenic fungi (Fusarium oxysporum f. sp. cubense race 4 (Foc4) and Rhizoctonia solani (R. solani)) were systematically assessed. The aggregation of polymers in water was characterized by the critical micelle concentration (CMC) values, zeta potentials, and particle sizes and distributions. All PDMS-g-AH had positive zeta-potential values and exhibited high micellar stability in water. At the same time, the aggregation characteristics of polymers are affected by the structure and molecular weight of polymers. Small aggregates and high zeta-potentials interacted easily with the microbial cell membranes, which affected the antimicrobial activity together. These results indicated that the block type of PDMS-g-AH, i.e., PDMS-b-AH, showed better antimicrobial activities than the random type (PDMS-co-AH), and the optimal antimicrobial activities were obtained for moderate polymer chain length (about 5 kDa). This work reveals the relationship between the chemical structure of PDMS-g-AH, their aggregation behavior in water as well as interaction with biological membranes during the sterilization process, which provides the potential applications as fungicidal agents for effectively controlling plant diseases, such as rice sheath blight and banana Fusarium wilt.

The Effect of Banana Rhizosphere Chemotaxis and Chemoattractants on Bacillus velezensis LG14-3 Root Colonization and Suppression of Banana Fusarium Wilt Disease

Fusarium oxysporum f. sp. cubense (Foc) causes banana Fusarium wilt disease, which is a destructive soil-borne disease. Many plants can recruit rhizosphere microorganisms using their root exudates, thereby shaping the rhizosphere microbiome to resist pathogen infection. Therefore, this study was conducted to explore the role of root exudates in the process of biocontrol strain colonization and resistance to pathogens. In this study, the banana root exudates used as chemoattractants were obtained by hydroponics. Bacillus velezensis strain LG14-3 was isolated from the infected area of the root system of banana and showed significant chemotaxis to banana root exudates and strong inhibition of Fusarium oxysporum f. sp. cubense. Further analysis found that LG14-3 showed chemotaxis toward the components of banana root exudates, such as citric acid, succinic acid, glycine, D-galactose and D-maltose, and glycine and citric acid, which resulted in more significant chemotaxis of LG14-3. Moreover, banana root exudates enhanced the swarming motility and biofilm formation of LG14-3. Pot experiments showed that glycine and citric acid enhanced the colonization ability of Bacillus velezensis LG14-3 in the banana rhizosphere and reduced the disease severity index of banana fusarium wilt. Glycine and citric acid enhanced the growth-promoting ability of LG14-3 under pathogen stress. Our results showed that the addition of chemotactic substances enhanced the biocontrol potential of Bacillus velezensis LG14-3 to prevent banana Fusarium wilt.

Construction of a compound microbial agent for biocontrol against Fusarium wilt of banana.

Banana wilt caused by Fusarium oxysporum f. sp. cubense has devastated a large number of banana plantations worldwide. Biological control is a possible method to conquer this disease. However, the control effect was often low and unstable while a single biocontrol strain had been applied in the field. Therefore, this study aimed to construct an effective compound microbial agent to control Fusarium wilt of banana (FWB) in the field. In addition to it, the compounding strategy of combining single strains for improving the control effect was investigated. Based on the compatibility test, five representative biocontrol strains were selected for the combination of all possible permutations. The pot experiment indicated that every biocontrol strain and their 26 combinations could control FWB to varying degrees. The control effect of combinations on FWB was higher than that of a single strain. In terms of the number of combinatorial biocontrol strains, the control effect of the four-strain combinations was the highest. According to the taxonomic differences of the five biocontrol strains, 26 biocontrol strain combinations could be divided into four groups. Among the strains in the combination, the larger the taxonomic differences the more easily it was to obtain a higher control effect. To obtain stable and efficient combinations, eight combinations were selected out and evaluated for their effectiveness in controlling FWB in different type soil. Compared with the other seven combinations, the four-strain combination T28 (Pt05 + Bc11 + Ba62 + gz-2) got the highest and stablest control effect in the four types of soil in greenhouse. And then the control effect of combination T28 was evaluated in field conditions, compared with commercially agents Bacillus subtilis, Trichoderma harzianum, and carbendazim. After four consecutive applications in the field, the control effect of T28 against FWB was the highest, reaching 57.14%. The results showed that combination T28 had a good application prospect, and the finding provided a reference for the construction of compound microbial agents.

Fluorine-containing amphiphilic quaternary ammonium salts for the suppression of Banana fusarium wilt

As the pathogen of banana Fusarium wilt, Fusarium oxysporum f. sp. cubense race 4 (Foc4) has the strongest toxicity and pathogenicity due to its long-term viability in soil, but there is still no effective way to control it at present. Based on the activity parameters of polymeric quaternary ammonium salt in our previous work, this paper hopes to enhance the amphiphilicity of polymeric quaternary ammonium salt by introducing a fluoroalkyl group to improve the antifungal property of polymeric quaternary ammonium salt and achieve stable adsorption and long-term inhibition of saprophytic Foc4 conidia in soil. Here, we prepared a series of fluorine-containing ammonium salts with random and block structures by atom transfer radical polymerization (ATRP), and we systematically studied the effects of the introduction of fluoroalkyl groups, the proportion of hydrophobic segments and polymer structure on micelle properties, antifungal properties, adsorption, migration and long-term antifungal properties against Foc4 in soil. Finally, the preferred polymeric quaternary ammonium salts were selected for pot experiments in the prevention and control of banana Fusarium wilt caused by Foc4, and positive experimental results were achieved. In conclusion, we made an exploratory attempt at the practical application of polymeric amphiphilic quaternary ammonium salt in plant disease control.

Genome Sequence Data Reveal at Least Two Distinct Incursions of the Tropical Race 4 Variant of Fusarium Wilt into South America.

The global banana industry is threatened by one of the most devastating diseases: Fusarium wilt of banana. Fusarium wilt of banana is caused by the soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), which almost annihilated the banana production in the late 1950s. A new strain of Foc, known as tropical race 4 (TR4), attacks a wide range of banana varieties, including Cavendish clones, which are the source of 99% of banana exports. In 2019, Foc TR4 was reported in Colombia, and more recently (2021) in Peru. In this study, we sequenced three fungal isolates identified as Foc TR4 from La Guajira (Colombia) and compared them against 19 whole-genome sequences of Foc TR4 publicly available, including four genome sequences recently released from Peru. To understand the genetic relatedness of the Colombian Foc TR4 isolates and those from Peru, we conducted a phylogenetic analysis based on a genome-wide set of single nucleotide polymorphisms (SNPs). Additionally, we compared the genomes of the 22 available Foc TR4 isolates, looking for the presence-absence of gene polymorphisms and genomic regions. Our results reveal that (i) the Colombian and Peruvian isolates are genetically distant, which could be better explained by independent incursions of the pathogen to the continent, and (ii) there is a high correspondence between the genetic relatedness and geographic origin of Foc TR4. The profile of present/absent genes and the distribution of missing genomic regions showed a high correspondence to the clades recovered in the phylogenetic analysis, supporting the results obtained by SNP-based phylogeny.

Survey, identification and management of Fusarium wilt of banana in Tamirabarani tract of Southern districts of Tamil Nadu

In Tamil Nadu state, Thoothukudi district ranked second in banana production and especially the Tamirabarani tract of Thoothukudi and Tirunelveli districts are known for the production of various banana cultivars like Rasthali, Andhra Kozhi, Karpooravalli, Neypoovan, Poovan, Peyan and Chakkai. Among these varieties, cultivation of Rasthali faces 50-60% yield loss due to the incidence of Fusarium wilt disease. As the farmers have been practising ratooning for 6-7 year continuously which enhances the inoculum load of the pathogen and make the plantains succumb to Fusarium oxysporum f. sp. cubense (Foc). Studies carried out on different treatments in the management of Fusarium wilt of banana, Trichoderma sp. Tsp1(ALG) showed a maximum reduction of mycelial growth of Foc (72.18%) over control which was on par with Pseudomonas fluorescence 1(Pf1). Under pot culture conditions the combination of three treatments, Tsp1(ALG)+Pf1+ neem cake excelled and showed an 80% reduction of wilt incidence. A multifaceted approach comprising the application of biocontrol agents (Trichoderma sp.) + Pseudomonas sp. 1 (TNAU) and organic amendments was found to be the best management practice in containing the wilt.

Antifungal Mechanism of Metabolites from Newly Isolated Streptomyces sp. Y1-14 against Banana Fusarium Wilt Disease Using Metabolomics.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is one of the most destructive banana diseases in the world, which limits the development of the banana industry. Compared with traditional physical and chemical practices, biological control becomes a promising safe and efficient strategy. In this study, strain Y1-14 with strong antagonistic activity against Foc TR4 was isolated from the rhizosphere soil of a banana plantation, where no disease symptom was detected for more than ten years. The strain was identified as Streptomyces according to the morphological, physiological, and biochemical characteristics and the phylogenetic tree of 16S rRNA. Streptomyces sp. Y1-14 also showed a broad-spectrum antifungal activity against the selected 12 plant pathogenic fungi. Its extracts inhibited the growth and spore germination of Foc TR4 by destroying the integrity of the cell membrane and the ultrastructure of mycelia. Twenty-three compounds were identified by gas chromatography-mass spectrometry (GC-MS). The antifungal mechanism was investigated further by metabolomic analysis. Strain Y1-14 extracts significantly affect the carbohydrate metabolism pathway of Foc TR4 by disrupting energy metabolism.

Comparative Transcriptome Analysis Unravels the Response Mechanisms of Fusarium oxysporum f.sp. cubense to a Biocontrol Agent, Pseudomonas aeruginosa Gxun-2

Banana Fusarium wilt, which is caused by Fusarium oxysporum f.sp. cubense Tropical Race 4 (FOC TR4), is one of the most serious fungal diseases in the banana-producing regions in east Asia. Pseudomonas aeruginosa Gxun-2 could significantly inhibit the growth of FOC TR4. Strain Gxun-2 strongly inhibited the mycelial growth of FOC TR4 on dual culture plates and caused hyphal wrinkles, ruptures, and deformities on in vitro cultures. Banana seedlings under pot experiment treatment with Gxun-2 in a greenhouse resulted in an 84.21% reduction in the disease. Comparative transcriptome analysis was applied to reveal the response and resistance of FOC TR4 to Gxun-2 stress. The RNA-seq analysis of FOC TR4 during dual-culture with P. aeruginosa Gxun-2 revealed 3075 differentially expressed genes (DEGs) compared with the control. Among the genes, 1158 genes were up-regulated, and 1917 genes were down-regulated. Further analysis of gene function and the pathway of DEGs revealed that genes related to the cell membrane, cell wall formation, peroxidase, ABC transporter, and autophagy were up-regulated, while down-regulated DEGs were enriched in the sphingolipid metabolism and chitinase. These results indicated that FOC TR4 upregulates a large number of genes in order to maintain cell functions. The results of qRT-PCR conducted on a subset of 13 genes were consistent with the results of RNA-seq data. Thus, this study serves as a valuable resource regarding the mechanisms of fungal pathogen resistance to biocontrol agents.

Evaluation of Resistance of Banana Genotypes with AAB Genome to Fusarium Wilt Tropical Race 4 in China.

Banana cultivars with the AAB genome group comprise diverse subgroups, such as Plantain, Silk, Iholena, and Pisang Raja, among others, which play an important role in food security in many developing countries. Some of these cultivars are susceptible to Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), the most destructive pathogen threatening banana production worldwide, and some of them are still largely unknown. We evaluated the resistance of 37 banana genotypes, including Plantain, Silk, Iholena, Maia Maoli/Popoulu, Pisang Raja, Pome, and Mysore, to Foc TR4 under both greenhouse and field conditions. Genotypes from the Silk and Iholena subgroups were highly susceptible to Foc TR4. Pome and Mysore showed resistance and intermediate resistance, respectively. However, Pisang Raja ranged from susceptible to intermediate resistance. One cultivar from the Maia Maoli/Popoulu subgroup was highly susceptible, while the other displayed significant resistance. Most Plantain cultivars exhibited high resistance to Foc TR4, except two French types of cultivar, 'Uganda Plantain' and 'Njombe N°2', which were susceptible. The susceptibility to Foc TR4 of some of the AAB genotypes evaluated, especially Plantain and other cooking bananas, indicates that growers dependent on these varieties need to be included as part of the prevention and integrated Foc TR4 management strategies, as these genotypes play a crucial role in food security and livelihoods.

First Report of Fusarium Wilt of Iholena Banana (Musa spp.) Caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 in China.

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), has been considered as the most devastating disease affecting bananas (Musa spp.) worldwide. A highly virulent strain of Foc, known as tropical race 4 (TR4), has been detected in the southeast Asia in the 1990s, and has since spread to western Asia, Australia, the Middle East, southern Africa, and South America (Viljoen et al. 2020). Foc TR4 can cause severe yield losses in Cavendish (AAA), Gros Michel (AAA), Silk (AAB), Pisang Awak (ABB) and Bluggoe (ABB) bananas (Ploetz et al. 2006). However, cooking bananas such as plantain (AAB) and Matooke (AAA) bananas, appear to be resistant (Zuo et al. 2017). Iholena bananas (AAB), a subgroup of varieties related to plantains (also known as Pacific plantains), is an important staple food in the Pacific Islands where it was domesticated. It is also popular in Peru, probably due to its nutritional value (Kepler et al. 2011) and is wildly cultivated in other South American countries (Dita et al. 2013). In December 2019, typical symptoms of banana Fusarium wilt were observed on Iholena accession 'Pacific Plantain' (ITC0210) in experimental fields located in Dongguan, Guangdong Province of China. The symptoms included leaf yellowing and pseudostem splitting. The vascular tissue inside the pseudostems was dark red to brown, and the inner rhizomes yellowish-brown. Vascular tissues from three diseased plants were sampled aseptically and placed on potato dextrose agar (PDA) containing 0.05 g/liter kanamycin. Fungal colonies typical of F. oxysporum developed rapidly, with purple-tinged white aerial mycelia and an abundance of microconidia borne in false heads on short microconidia (Nelson et al. 1983). Chlamydospores were produced singly or in pairs in hyphae and macroconidia. Molecular identification was performed using Foc race 4-specific primers (Lin et al. 2009), Foc TR4-specific primers (Dita et al. 2010), Foc race 1 and Foc STR4-specific primers (Ndayihanzamaso et al. 2020). Amplicons of expected sizes were obtained for Foc TR4 and race 4, but not for Foc race 1 and STR4. Sequencing of theITS and 18S rDNA from the three Iholena isolates and BLAST result showed a 100% similarity to the Foc TR4 reference sequences in GenBank (Foc II5, PRJNA73539 and PRJNA56513) to prove that the isolates were Foc TR4. Pathogenicity of the three isolates from Iholena bananas was determined by infecting 4-month-old Cavendish cv. 'Grand Nain' bananas and three Iholena accessions, 'Pacific Plantain' 'Tigua' and 'Uzakan', under greenhouse conditions by root immersion in a Foc conidial suspension and soil drenching at 106 conidia/ml (Dita, 2010). Control plants were treated with sterile distilled water. Three replications of five plantlets were used for each accession. After 35 days, the inoculated plantlets developed typical Fusarium wilt symptoms such as yellowing of the older leaves and discoloration of the inner rhizome. The control plants did not develop symptoms. To complete Koch's postulates, the fungus was re-isolated from inoculated plants and identified as Foc TR4 by PCR (Dita et al, 2010). The susceptibility of 'Tigua' and 'Uzakan' was also confirmed in Foc TR4-infested field trials, with both accessions developing severe Fusarium wilt symptoms. The susceptibility of Iholena bananas to Foc TR4 is of significant concern to all countries where this subgroup is cultivated for major food source, including Peru and other South American countries.

The Population of Fusarium oxysporum f. sp. cubense in Brazil Is Not Structured by Vegetative Compatibility Group or by Geographic Origin.

Fusarium wilt, caused by the soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), is considered one of the most destructive diseases of bananas in Brazil. In this study, a collection of 194 monosporic isolates from several banana-producing regions located in different climatic zones along a south-to-north transect in Brazil was formed to assess the genetic structure of the population of Foc. The isolates underwent pathogenicity tests, PCR diagnosis for the detection of tropical race 4, and screening of SIX homolog genes that produce putative effector proteins. The vegetative compatibility group (VCG) of 119 isolates was determined by pairing against 17 internationally known VCG-tester strains. A group of 158 isolates was selected for simple sequence repeat (SSR) genotyping. There was moderate diversity of Foc in Brazil. Eight VCGs were identified: 0120, 0122, 0124, 0125, 0128, 01215, 01220, and 01222, of which 78% of isolates belong to a single VCG, whereas 22% of isolates are assigned to multiple VCGs, belonging to complexes of VCGs. The distribution of VCGs is uneven and independent of the banana genotype. The isolates of a VCG shared a similar profile of SIX homologs, but there was no association with geographic region. Four SSR loci were polymorphic, and, on average, 7.5 alleles were detected per locus. Thirty-five multilocus genotypes (MLGs) were identified. There was no association between VCG and MLGs, and no genetic structure of the population of Foc in Brazil was detected.

Characterization and Antagonistic Effect of Culturable Apple-Phyllosphere Endophytic Bacteria from the Cold Plateau in Yunnan, China

The endophytic bacteria in apple leaves from apple-producing areas of Yunnan, China were isolated and identified on the basis of bacterial colony morphology and nucleotide sequences of 16S rRNA and rpoB genes. The endophytic bacterial isolates with nitrogen, phosphorus, and potassium utilization abilities were screened by culturing on functional media. A total of 5709 isolates of culturable endophytic bacteria (CEB) were isolated from 30 apple leaf samples collected from different regions. A total of 39 CEB representative isolates were identified as Bacillus velezensis, B. subtilis, B. licheniformis, B. safensis, B. pumilus, and Priestia megaterium. Among them, B. velezensis and B. subtilis were the main CEB, accounting for 55.00% and 34.37%, respectively, which exhibited potential inhibition on not only the main apple disease pathogens of Alternaria alternata, Valsa mali, Fusarium oxysporum, and Rosellinia necatrix, but also some important and uncontrollable phytopathogens, including F. oxysporum f. sp. cubense that causes banana Fusarium wilt, and Phytophthora nicotianae that causes tobacco black shank. Among these isolated endophytic bacteria species, a total of 10 strains, including b3, b4, b16, b17, b20, and b23 of B. subtilis, b7, b24, and b28 of B. licheniformis, and b38 of B. velezensis, can fix nitrogen; 8 strains, including b7 and b28 of B. licheniformis, b5, b10, and b23 of B. subtilis, b8 of B. safensis, and b6 of Priestia megaterium, could dissolve inorganic phosphorus; 11 strains, including b9, b12, b14, b30, b34, and b43 of B. velezensis, b6 of Priestia megaterium, and b17, b18, b20, and b26 of B. subtilis, could degrade organic phosphorus; and 5 strains, including b4, b5, and b26 of B. subtilis, and b7 and b28 of B. licheniformis could dissolve potassium. These strains are valuable resources of endophytic bacteria that have adapted to the ecological environment of the Cold Plateau apple-production area and could be used as plant disease biocontrol agents and biofertilizers of crops. The culturable phyllosphere endophytes in apple leaves relate to geographic locations, apple varieties, and environment, providing the basis to explain the mechanisms underlying the establishment of apple endophyte diversity and may help to devise apple disease management strategies.

Multi-site fungicides suppress banana Panama disease, caused by Fusarium oxysporum f. sp. cubense Tropical Race 4.

Global banana production is currently challenged by Panama disease, caused by Fusarium oxysporum f.sp. cubense Tropical Race 4 (FocTR4). There are no effective fungicide-based strategies to control this soil-borne pathogen. This could be due to insensitivity of the pathogen to fungicides and/or soil application per se. Here, we test the effect of 12 single-site and 9 multi-site fungicides against FocTR4 and Foc Race1 (FocR1) in quantitative colony growth, and cell survival assays in purified FocTR4 macroconidia, microconidia and chlamydospores. We demonstrate that these FocTR4 morphotypes all cause Panama disease in bananas. These experiments reveal innate resistance of FocTR4 to all single-site fungicides, with neither azoles, nor succinate dehydrogenase inhibitors (SDHIs), strobilurins or benzimidazoles killing these spore forms. We show in fungicide-treated hyphae that this innate resistance occurs in a subpopulation of "persister" cells and is not genetically inherited. FocTR4 persisters respond to 3 μg ml-1 azoles or 1000 μg ml-1 strobilurins or SDHIs by strong up-regulation of genes encoding target enzymes (up to 660-fold), genes for putative efflux pumps and transporters (up to 230-fold) and xenobiotic detoxification enzymes (up to 200-fold). Comparison of gene expression in FocTR4 and Zymoseptoria tritici, grown under identical conditions, reveals that this response is only observed in FocTR4. In contrast, FocTR4 shows little innate resistance to most multi-site fungicides. However, quantitative virulence assays, in soil-grown bananas, reveals that only captan (20 μg ml-1) and all lipophilic cations (200 μg ml-1) suppress Panama disease effectively. These fungicides could help protect bananas from future yield losses by FocTR4.